A Long Term Evolution-Advanced (LTE-A) system may support a transmission method for performing Uplink Control Information (UCI) feedback on the basis of carrier groups, i.e., dividing aggregation carriers into a plurality of carrier groups and performing the UCI feedback within each carrier group. An uplink carrier is designated in each carrier group, so as to feed back the UCI of the carrier group on the uplink carrier via a Physical Uplink Control Channel (PUCCH). Also, the UCI corresponding to the carriers in each carrier group may be fed back on a Physical Uplink Shared Channel (PUSCH) for the carrier group. Hence, for a User Equipment (UE), there may exist in an identical uplink subframe a plurality of PUCCH(s) and/or PUSCH(s) carrying the UCI for different carrier groups.
The UCI may include Acknowledgement/Non-Acknowledgement (ACK/NACK), Chanel State Information (CSI) and Scheduling Request (SR), and the CSI may include periodic CSI and aperiodic CSI.
LTE-A Release-10 (Rel-10) and Release-11 (Rel-11) systems merely support the PUCCH transmission on an uplink Primary Component Carrier (PCC). For the UE, the PUSCH transmission may exist in an identical uplink subframe on a plurality of uplink carriers simultaneously, but the UCI transmission may be carried by merely one of the PUSCH(s). In the case of the co-existence of the PUCCH(s) and the PUSCH(s) carrying the UCI, the UCI carried by the PUCCH(s) and the PUSCH(s) is of different types. For example, the PUCCH may carry the ACK/NACK, while the PUSCH carries the periodic CSI. In other words, the UCI carried by the PUCCH(s) is of a more important type, and there will not exist such a situation where the UCI of an identical type is carried simultaneously by the PUCCH(s) and/or PUSCH(s) or the UCI carried by the PUSCH(s) is of a more important type. Hence, during the power control, it is required to preferentially ensure that the transmission power for the PUCCH(s) is not reduced.
In the LTE-A system, there is the data transmission simultaneously over the PUCCH(s) and/or PUSCH(s) carrying the UCI, and it is not defined in the original system about how to reduce the power for the PUCCH(s) and/or PUSCH(s) carrying the UCI in the case of constrained power. In addition, the PUCCH(s) and/or PUSCH(s) may carry the UCI of an identical type or different types, e.g., they may carry the ACK/NACK, or one of the PUCCH(s) (or PUSCH(s)) may carry the periodic CSI for one carrier group while another one of the PUCCH(s) (or PUSCH(s)) may carry the ACK/NACK for another carrier group. In the case that the power is constrained but a power control scheme for the original system is still used, i.e., the transmission power for the PUCCH(s) is preferentially granted, the transmission of the UCI of an important type, e.g., the SR or the ACK/NACK may be adversely affected due to the reduction in the transmission power, and thereby the entire transmission performance for the system will be adversely affected.
In a word, there is currently no uplink power control scheme in the case that the UE supports the independent UCI feedback for different carrier groups.